The skies around Syria are even emptier than usual as airlines try to keep clear of a potential US airstrike on Syria.Planes have been avoiding war-torn Syrian airspace for years, but new warnings expanded the danger zone.Flight regulators told planes to steer clear of the eastern Mediterranean and Cyprus, where US and Russian naval assets are based.Donald Trump is considering a punitive strike on Bashar al-Assad's regime in retaliation over a reported chemical attack on civilians.